Long-term allograft survival is readily achieved in murine cardiac allograft recipients, but very little is known about the mechanisms by which this allograft acceptance is induced or maintained. We have developed a testable, working paradigm of cardiac allograft acceptance. This paradigm holds that allograft acceptance involves immune processes that actively protect allografts. We believe that one manifestation of this alloprotective process, the phenomenon of linked antigen non-responsiveness, holds the key to understanding allograft acceptance. The proposed studies will investigate important aspects of the alloprotective responses that develop in allograft recipients. Specific Aim 1: To evaluate the contributions of three intriguing cell types to the initiation of allograft acceptance responses. These are addressed as the "memory hypothesis", the "gamma/delta hypothesis", and the "NKT hypothesis". In general, we will use cell transfer studies with SCID mice to determine the role of memory T cells, gammadeltaT cells or NKT cells in the generation of alloprotective activity, ie., linked DTH non-responsiveness or cardiac allograft acceptance. Specific Aim 2: To evaluate two non-competing mechanisms by which allograft acceptance is maintained. These are addressed as the "cytokine synergy hypothesis" and the "protected compartment hypothesis". In general, we will use cytokine knock-out mice and anti-cytokine antibodies to dissect the roles of TGFbeta, IL10 and IL4 in the expression of alloprotective activity (linked DTH non-responsiveness and cardiac allograft acceptance). We will also determine whether new alloprotective mechanisms independent of these cytokines are installed in accepted allografts over time. Specific Aim 3: To identify the cytokine environment necessary for the in vitro generation of alloprotective T cells that can be transferred into allograft recipients to promote cardiac allograft acceptance. Initially, these studies will use IL10 to drive alloantigen- stimulated splenic T cells towards alloprotective behavior. Specific Aim 4: To evaluate and optimize the experimental system in which tolerization to BSA, a foreign protein unrelated to an allograft, can be used to promote linked non-responsiveness to graft alloantigens, and thus educate an allograft recipient toward allograft acceptance. This represents a novel therapeutic approach that uses BSA as a "vaccine" for transplant recipients. Routine molecular genetic methods would allow us to explore the potential of this vaccine strategy for use as a potential gene therapy in transplant recipients. Finally, we will evaluate the effects of concurrent infection with murine influenza virus on he survival of the graft and recipient in mice that are being educated with BSA for allograft acceptance.